Generic way for mitigating incompatible api-resource versions

[ReToCode]

Maybe a bit far fetched, but could be interesting in the future.

As kcp is going to manage a lot of clusters, it'll be inevitable to have multiple different kubernetes versions with incompatible api-resources. Workspaces and Sharding can help to reduce it, but it would be great to have a generic, automated way to mitigate those differences.

Similar to #97 (comment) CRD authors (and K8s built-in types) would specify transformations/patches between different versions. kcp would apply those transformations depending on the target clusters api-resource version.

This would allow kcp users, combined with cross-cluster ingress routing, to migrate workloads fully automated to new kubernetes cluster versions. And thus, having a completely immutable, rolling-update-like cluster operation experience.

WDYT?

@smarterclayton a few years back, we discussed something like this over beers (https://github.com/ReToCode/openshift-cross-cluster-loadbalancer)
@eberlec FYI.